Reactions of nitriles with binuclear rhodium hydrides. The stepwise reduction of a carbon–nitrogen triple bond at two metal centres

Abstract

The reaction of simple nitriles, R′CN (R′ = CH3, Ph, o-tol) with the electron-rich binuclear rhodium hydride derivatives [(R2PCH2CH2PR2)Rh]2(μ-H)2 (R = Pri: [(dippe) Rh]2(μ-H)2; R = OPri: [(dipope)Rh]2(μ-H)2) results in the formation of alkylideneimido derivatives [(R2PCH2CH2PR2)Rh]2(μ-H)(μ-N=CHR′), apparently by insertion of the nitrile moiety into a bridging hydride bond; this was confirmed by the reaction of nitriles with the dideuteride [(dippe)Rh]2(μ-D)2, which resulted in the formation of [(dippe)Rh]2(μ-D)(μ-N=CHR′). Further reduction can take place by addition of H2 to generate the corresponding amide hydride derivatives [(dippe)Rh]2(μ-H)(μ-NHCH2R′); this represents an overall stoichiometric reduction of a nitrile to a coordinated amide at a binuclear centre. These same amido-hydride complexes can be accessed by addition of amine to the starting binuclear rhodium hydride derivatives. The X-ray structure of [(Pri2PCH2CH2PPri2)Rh]2(μ-H)(μ-N=CHCH3) was undertaken to confirm the structure of these particular intermediates. Crystals of this material are monoclinic, a = 19.036(2), b = 15.139(1), c = 13.604(1) Å, β = 104.119(7)°, Z = 4, space group P21/c. The structure was solved by heavy atom methods and was refined by full-matrix least-squares procedures to R = 0.038 and Rw = 0.041 for 5814 reflections with I ≥ 3σ(I).